I always thought the engineers kept the rake and trail exactly the same on the L and the G, so there wasn't any difference in handling. Maybe a slightly different gear ratio in the pumpkin and a smaller rear wheel made it feel like it handled differently?
Correct; despite the oft-repeated legends, there is zero difference in handling capabilities or geometry.
Source: me riding my G and a couple of GLs that belong to friends back to back, and pushing them fairly hard.
They do feel somewhat different because the seating position is different on the "L" model, and you're more or less locked into one place by the stepped seat. The advantages, of course, are less of a reach to the pegs and to the ground, so folks who are shorter than average might prefer the L. The stock handlebars on both the G and GL were evil abominations, so you have to factor that into evaluating the ergos and handling as well. The handlebars have pretty much all been changed, because the bikes are literally intolerable otherwise.
The other very minor difference is that most GL models used a 16" rear wheel, while the G used a 16" rear wheel. This gave very slightly better acceleration in lower gears. Also, in some GL engines, there was a one tooth difference in the fifth gear, and so RPM in fifth gear ended up almost the same. Source: there's a GL engine in my G. I noticed that RPM on the highway was slightly lower after the transplant, and did a lot of research in the fiches.
To sum up: with the usual necessary suspension upgrades (fresh shocks and fork springs at minimum), and allowing for the ergonomic differences, the G and GL models handle identically. Cornering clearance is identical, and as stated, despite the different forks, the frame angles are managed such that the rake and trail end up the same.
Also, bear in mind that Suzuki was the first to really figure out frame geometry; despite their high weight, the G and GL models handle superbly, far better than they have any right to.
Or rather, they CAN handle far better than expected. In bone-stock form, with bouncy, worn-out stock shocks, super-soft fork springs, and evil handlebars, they're as terrible as any other old neglected bike. Same goes for the brakes; with fresh, clean stock calipers and master cylinder, decent new pads, and stainless lines, the stock brakes are actually pretty impressive for the early '80s, and perfectly workable and safe for modern riding.
For whatever reasons, the GL models sold a lot better back in the disco/post-disco era. These days, of course, the more timeless styling of the G model is preferred, but there are a lot more GLs lying around. All else being equal, they can and do function exactly the same, but there are important ergonomic differences you need to bear in mind.
As far as the chain drive "L" and "E" models, I don't have firsthand experience with comparing them back to back, so I'll defer to anyone who does have such experience. But I would guess that the situation is pretty much the same.